1. Field of The Invention
This invention relates to a robot welding gun unit which is a robot equipped with a welding gun.
2. Description of The Prior Art
Conventional robot gun units had a problem that when it proceeded to next welding operation without compensating for the wear of electrodes in preceding welding operation, which caused the formation of a gap between an electrode on the side of a fixed arm and a weldment, the gap being formed as the fixed electrode was worn away, and which caused the deformation of the weldment when the same was clamped between the electrodes for welding. In order to solve the problem, the welding gun was equipped with an equalizer unit and the gun body was supported by a spring at the time of welding to prevent the weldment from being deformed. In case of a robot welding gun, however, the welding posture of the weldment varied according to the different positions and shapes of the weldment so that the spring sometimes did not work effectively and it was difficult to adjust the spring.
Each of some robot welding guns clamps the weldment between an electrode on the side of a fixed arm and a presser electrode for welding with the fixed arm side electrode being always in contact with a surface of the weldment and with the presser electrode being advanced toward the weldment by a robot instead of the equalizer unit described above (e.g., the Japanese Patent Laid-Open Publication No. 2 179363).
The robot welding gun disclosed in the above publication, however, has a problem that it is very troublesome in control since an electrode on the side of the fixed arm is always in contact with a surface of the weldment so that the robot has to be moved variously in accordance with the wearing amount of the electrode although the generation of the gap due to the wear of the electrode can be prevented.